An emergency braking system for trucks is known from German Published Patent Application No. 37 34 489 in which a supplementary servo braking device is independent of the normal braking device of the front wheels and the rear wheels and which is effective until the vehicle has come to a standstill or is at least slowed down to a controllable driving state. The power for controlling the supplementary servo braking device is obtained from a part of the truck which necessarily rotates when the truck is in motion. The supplementary servo braking device has a chargeable power accumulator (pressure holding device) for this purpose. Pressure charging of the pressure accumulator takes place in a moving truck via a necessarily rotating part of the truck. For example, the input shaft or the output shaft of the universal joints or the drive shaft are intended for this purpose. The supplementary servo braking device is intended as an emergency braking system which is actuated by operating the emergency switching device in the driver's cab. Independently of the emergency switching device operatable by the driver, the emergency braking system may be actuated automatically if the analysis of the rotational speed signal of one axle indicates that the normal servo braking device is malfunctioning.